This invention generally relates to a system for propelling an elevator. More particularly, this invention relates to a system for providing traction between a sheave and a belt or rope.
Elevator systems typically include a mechanism for moving the elevator cab as desired within a hoistway, for example. Some systems include a counterweight and sheave arrangement that moves a counterweight and cab through the hoistway between landings as needed. Other systems, commonly referred to as xe2x80x9cself-propelledxe2x80x9d systems include a driving mechanism that is supported for movement with the elevator cab through the hoistway.
The load of the counterweight and the cab in counterweighted systems provides the necessary traction between the rope or belt and the driving sheaves to achieve proper elevator operation. In order to achieve a desired amount of traction, the mass of the cab and counterweight typically is quite large. Larger loads introduce additional wear on the belts or ropes.
There are several possible disadvantages associated with the traditional approach when additional traction is required. One is that adding additional mass introduces additional material and labor cost during assembly, for example. Additionally, multiple belts or ropes are required and the corresponding sheaves must have multiple grooves to accommodate the multiple ropes. This adds complexity and material cost to the system. Another drawback associated with such systems is that the belts or ropes typically are maintained under constant tension, which introduces the possibility for additional wear on the belts, requiring more frequent maintenance or replacement.
There is a need for an improved system to provide appropriate traction in an elevator system for moving the cab as desired. This invention addresses that need while avoiding the shortcomings and drawbacks of the prior attempts discussed above.
In general terms, this invention is an assembly for propelling an elevator cab. The assembly includes at least one tension device that biases an elevator rope or belt against a driving sheave. The tension device includes a plurality of rolling members that are supported in a selected position relative to the driving sheave. The rolling members preferably are passive and roll responsive to relative movement between the driving sheave and the elevator rope or belt. A tension belt is associated with the rolling members. The tension belt engages the elevator rope or belt and applies a force that biases the rope or belt against the driving sheave.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiments. The drawings that accompany the detailed description can be briefly described as follows.